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Topic: Question of the Week - Old Version (Read 179356 times)

The Wiki explanation, however, is focused more on the universe's expansion, and the consequent Doppler redshift of light from distant stars (frequency and intensity becomes lower and lower with distance).

jolly

i guess its because as your skin gets cold it shrinks, as all things do, and as it shirks it makes little hills with air between them which helps them retain heat when used in conjuction with the bodies hairs, the bodies heat then has to travel up through these little hills as if theres extra skin there. so it could be like the body gives itself an extra two or three layers of skin slowing down heat loss; and keeping you warmer just long enought for you to find a jumper.lol best guess why is it?

Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.

Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.

Do you mean experimentally? Of course not, since, AFAIK, gravitational waves hasn't been even detected yet.

lyner

As a measurement exercise, it is a nightmare. There is so much 'gravitational interference' from every other mass in the universe. The waves are expected to be very small and v e r y l o w f r e q u e n c y. If they were easy to spot, we would have seen them already.If you could get near a large binary star system, orbiting around its centre of mass, or a couple of black holes interfering with each other, - better, still , a supernova in our back yard, you would be in a better position to detect these waves (if, of course, they exist). The LIGO (Laser Interferometer Gravitational-Wave Observatory) is hoping to detect gravitational waves by tiny amounts of movement between mirrors situated on the Earth and spaced by a few km. LISA (Laser interferometer space antenna) is planned in the fairly near future, which will detect the relative wobbling of a set of satellites - spaced by a few million km - as gravitational waves go past.Nothing to report yet but keep your fingers crossed and avoid slamming doors and general loud behaviour; that realy doesn't help the sensitive equipment.

lyner

There would be some directivity in the sensitivity of the measuring array, presumably. You could avoid Interference from Earth by looking 'tangentially', perhaps, and then pick your moments for measurement when you are not pointing at anything too close and 'noisy'. That's the technique for radio astronomy, after all, when your telescope is not steerable.I would like to know the effective 'beamwidth' of the detector; it could be pretty narrow in the case of the LISA system, because of the enormous aperture. LIGO is not that big, however. Just a lot less sensitive, I would guess.

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jolly

Sorry thats a silly question.Gravity does not have a speed. What are you really asking? Earth gravity I suppose your talking about. It depends on the mass, different masses are affected differently.The speed of an object affected by earths gravity?Gravity itself doesnt have a speed its a force- Not like light which is radiation and has a speed of sorts.The question makes no sense.I mean black holes are the strongest gravity zones so are you asking a what speed are you pulled into them? because that again depends on the blackholes size.Are you asking at what speed you travel around blackholes- our sun travels about 42,000 miles an hour around our milky ways super massive black hole.But your question is about gravities speed and really it does not have a speed- In my opinion!

jolly

If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.

If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.

Sorry what I mean to say was "If the sun disapeared we wouldn't instantly verge off out of orbit instanly". It would verge off but not instantly." If you disagree with that you are wrong.

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jolly

Hello, if the sun disappeared there would be nothing to orbit.We would stop and go somewhere else- straight away. All the planets would fly off in the same direction. As the gravity from either the super massive blackhole at the milky ways core or a closer star would pull us in.What are you getting at that our speed and direction would remain the same for a while after the sun disappeared- that is totally un-true. The secound the sun disappeared the earth and other planets would pull towards the next high gravity source.So what you planning- Gonna destroy the sun as part of some stupid experiment, to see if your ideas are correct- Thats inteligent.

Even if you did fly off in the same dirrection for a while the gravity from near by stars would have an affect on you and slow you down.Gravity has no speed- It is intentanious- As its always there.

Yes, but when? If the sun moved, clearly orbits should vary as well. Let's say that the sun suddenly moves at 00:00. When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.

When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.

Right the affects of the super massive black hole at the center of the milkly way are felt throughtout our galaxcy- and beyond, as the next closest galaxcy is currently pulling towards us.Gravity is a constent- in other words it is just there- immediate- It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there. We are all caught with-in gravity; and the affect of gravity- will be instentaniuos as a result. Gravity is nothing like light. Once in position- its there- and as a result you will feel the affects straight away.Kinda like a spiders web. Light is radiation- Gravity is a force, Gravity once it has formed this spiders web- ergo, the area of its influence. will affect the things with-in its grasp straight away- and under those circumstances it has no speed it will be felt straight away.

Nic- the "speed of gravity" being discussed here is the speed at which the effect of gravity propagates through space. It has been suggested (derived from the maths) that this occurs at the speed of light (3x108 ms-1), but this hasn't been experimentally demonstrated (even assuming it's true this would be unsurprising since the experiments are a total nightmare due to the amount of competition from noise).9.8 ms-2 is the rate of acceleration due to gravity at the earth's surface, but the magnitude of that is due to the mass of the earth. On the moon it's about 1/6 of that value.

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics (if the effects of the Sun's gravity were to take 8 minutes to reach the Earth when it was first formed, but instantly disappears when the Sun disappears, then the Earth will have experienced the gravity of the Sun for 8 minutes less than the Sun was actually producing gravity - thus if there is a time lag in the effect of an increase of gravity, then there should be a similar time lag in it diminishing).

Light is merely a manifestation of the coulomb force (i.e. the force of an electric field). We perceive light as a wave because of the finite speed at which the coulomb force travels, and the effects of General Relativity upon the coulomb force emanating from a moving electrically charged particle (as one would have from the electrons moving in a piece of wire under the effect of an electric voltage applied to the wire).

Gravity does carry information, just as an electric field carries information.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon. In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans. Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence- that is not just our sun but also the other stars and the supermassive black hole at our galaxys core. Even if you remove the sun- the others still affect you instantly. In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon. In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans. Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.

Just because you do not notice an affect does not mean you are not being affected-e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding."honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects.

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence-

You don't need to observe its impact upon you (in any event, one cannot judge speed by looking at one location - one must observe at least two locations). Thus, if you observe the impact of changes in gravity upon two or more other bodies that are separated by a distance, you can tell if a change in gravity effects both objects at the same time, or it effects one object before the other.

In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

But you have not explained, if there is a delay in gravity reaching you when it is being 'formed', why that same delay should not exist when the gravity is being destroyed?

In your world, one could get the rather perverse situation where you detect the loss of a gravitational field before you detect the existence of a gravitational field (because the detection of the creation of the gravitational field took a finite time to reach you, but the collapse of the gravitational field arrived instantaneously).

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon. In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans. Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.

Just because you do not notice an affect does not mean you are not being affected-e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding."honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects.

If one takes a solipsistic approach, one can never actually prove anything beyond one's own mere existence; but in practical terms, there is overwhelming evidence that the tides are caused predominantly my the pull of the moon upon the Earth. You are correct that other bodies also have an influence, but the tides are so obviously synchronised to the orbit of the moon, and there is nothing else which is synchronised to the same extent with the ebb and flow of the tides, that I think we can regard it as highly improbable that the dominant force exerted upon the tides emanates from the Moon.

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